The present invention relates to improvements in apparatus and methods for separating solids and liquid mixtures, particularly for thickening thin slurries to form a concentrated sludge.
The invention improvement includes a solid bowl worm centrifuge separator which has a slurry admission, an outlet for a liquid fraction and an outlet for discharge of the concentrated sludge. In such a mechanism, thin slurries having a solid content or dry matter content of approximately 0.5% through 1.5% by weight, are generally received commercially from the floor of settling basins. For example, such slurries are produced in the biological treatment stage of sewage treatment plants. The major part of these thin slurries, which are laced with microorganisms, are pumped back into the settling basins as returned slurry. The remaining thin slurry, which is the excess slurry, must be withdrawn and must be concentrated before being introduced into a sludge digestion container. This slurry thickening often occurs in static slurry thickeners in which the slurry solids slowly settle as sediment and has a consistency which permits it to be subsequently pumped into a sludge digestion container.
It has been proposed to thicken thin slurries such as the excess slurries in a solid bowl worm centrifuge for the purpose of enhancing the separating power or in other words increasing throughput performance. It has been shown, however, that in a high performance worm centrifuge, the thin slurries are thickened through a sludge discharge having a dry matter content on the order of magnitude of approximately 8% through 10%. This thickened sludge can no longer be pumped. It must be conveyed to the sludge digesting container by involved equipment or an involved way. The operators of clarification plants require a thickened excess slurry that can be pumped into the digestion container. Further, the throughput power of even slurry thickening centrifuges is limited.
It is, therefore, an object of the present invention to provide a method and apparatus which can use centrifugal separating apparatus for the thickening of thin slurries where the throughput capability is substantially enhanced.
A further object is to provide a centrifugal thickening apparatus and process wherein the operation is assured and guaranteed that the concentrated sludge is always pumpable even with the use of a high performance worm centrifuge.